In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, increase in traffic within communications networks such as mobile broadband systems and an equally continuous increase in terms of the data rates requested by end-users (wireless terminals) accessing services provided by the communications networks may impact how cellular communications networks are deployed. One way of addressing this increase is to deploy lower-power network nodes, such as micro or pico radio base station (RBS) network nodes (hereinafter denoted PBS), within the coverage area of a macro cell served by a macro base station (MBS) network node. Examples where such additional network nodes may be deployed are scenarios where end-users are highly clustered. Examples where wireless terminals of end-users may be highly clustered include, but are not limited to, around a square, in a building, such as an office or a shopping mall, or along a road in a rural area. Such a deployment of additional network nodes is referred to as a heterogeneous or multi-layered network deployment, where the underlying layer of low-power micro or PBS network nodes does not need to provide full-area coverage. Rather, low-power network nodes may be deployed to increase capacity and achievable data rates where needed. Outside of the micro- or PBS-layer coverage, end-users would access the communications network by means of the overlaid macro cell.
Backhauling based on the Long Term Evolution (LTE) telecommunications standards may be carried either over normal IMT-bands, e.g. the 2.6 GHz frequency band, or by running LTE baseband communications on higher radio frequencies, such as in the 28 GHz frequency band. LTE based backhauling implies that the PBS network nodes are connected to a client node which is used to create a wireless link to a hub node.
In any of the above two cases, the wireless links are typically managed by LTE core control mechanisms. For example, the LTE Mobility Management Entity (MME) may be utilized for session control of the LTE links, and the Home Subscription Service (HSS) may be utilized for storing security and Quality of Service (QoS) characteristics of the wireless links of individual wireless end-user terminals embedded in the PBS network node.
Moreover, in practice more than one client node may connect to a common hub node. This implies support for Radio Resource Management (RRM) functions, such as scheduling and prioritization of the traffic to and from the different clients, at the hub node.
To each client node there might be several PBS network nodes, each of which may offer one or several different radio access technologies, such as based on the Universal Mobile Telecommunications System (UMTS), LTE, or IEEE 802.11X to the wireless end-user terminals of the end-users. Therefore there is a need to differentiate between the corresponding backhaul traffic to different nodes in the communications network. For example, any LTE compliant traffic may need to end up in nodes such as the serving gateway (S-GW) or the MME and any WiFi compliant traffic may end up in an edge router or an Evolved Packet Data Gateway (ePDG).
Moreover, for a given radio access technology (RAT), QoS differentiation is provided to the end-users (i.e., to the wireless end-user terminals of the end-users) so that e.g. guaranteed bitrate (GBR) services, such as voice calls, will not be disturbed by best effort (BE) services, such as web browsing. In order to enable this, QoS differentiation is needed also on the backhaul links.
If the wireless backhaul is based on LTE, there are tools that provide both the routing functions and QoS differentiation, such as the LTE bearer concept. Typically then, for each type of RAT, one GBR and one BE bearer are created on the backhaul links. In general there are different frameworks for prioritize between different traffic that can, for example determine if 10 Mbit/s Voice over IP (VoIP) data is more or less prioritized than 100 Mbit/s web-surfing data.
From an energy point of view, it may be beneficial to perform some kind of reconfiguration of the backhaul links in order to reduce the energy consumption. One example is to shut off one or more power amplifiers (Pas) at the hubs or and/or to shut off some hubs completely and let the clients connect to a fewer number of hubs.
From a capacity point of view, it may be beneficial to reconfigure the hubs in different ways. One example is to activate more hubs and redirect the client antennas to point towards other hubs so as to prevent, or at least mitigate, congestion and/or bottlenecks. Another way is for the hubs to create the transmission beams dynamically depending on the clients being served.
Typically, the different ways of reconfigurations imply temporary performance reduction or a delay in the available performance increase which will affect the end-user (wireless terminal) performance. FIG. 13 schematically illustrates a temporary performance drop which could occur during a backhaul radio access reconfiguration procedure. In a communications network undergoing an end-user access reconfiguration procedure such temporary performance drop may be especially severe if the backhaul system only reacts on the current load from the end-user part of the communications network. Depending on the functionality in the backhaul system and how fast it is enabled to react, different situations may occur. For example, in a worst case the wireless backhaul network notices a lowered end-user load during the end-user reconfiguration procedure and may thus determine to reconfigure to a lower capacity setting. For example, if the end-user reconfiguration is only a delay, the wireless backhaul network may perform the reconfigure procedure after the end-user reconfiguration is finished, thus having the impact that two reconfiguration delays occur before the switch to a higher capacity state is finished.
Hence, there is a need for an improved handling of reconfiguration in wireless backhaul networks.